The most common and most likely answer to this crossword clue is the 4 letter word WONT
I've seen this crossword clue in The Daily Telegraph
W
O
N
T
More clues leading to the result WONT
- Know about new habit
- Given time, current returns
- Petulant refusal is the custom
- Practice of few on Twitter
- Pull back, adopting new custom
- Succinct refusal as customary behaviour
- Tendency to abstain
- Word of defiance is a habit
- . Rule observed in revolutionary convent: no women
- Will not contracted to supply habit
Buddy explains!

The straight part
We know that "Word of defiance/a habit" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case word of defiance/a habit = wont.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does WONT mean?
WONT noun- One's habitual way of doing things; custom, habit, practice.
- To make (someone) used to; to accustom.
- To be accustomed (to something), to be in the habit (of doing something).
- Accustomed or used (to or with a thing), accustomed or apt (to do something).